The United States Department of Transportation requires periodic inspection of tube mounting threads on tube trailers used to transport compressed gases. In accordance with the current inspection procedure, to prevent the wear on the mounting threads of a tube from weakening the threaded connection to a point where safety may be compromised, the mounting threads on the tube must be inspected once every 10 years. The required inspection is a visual inspection using a Thread Pitch Gauge for measurement of the thread wear. Such visual inspection, however, requires removal of the mounting flanges. When evaluating the mounting threads on tubes, there are two basic categories of thread degradation that should be considered: generalized thread wear and isolated thread loss. Generalized thread wear is the erosion of the mounting threads over a significant area due to the relative motion between the tube and the mounting flange and is characterized by a measurably shorter height of the threads in the area engaged by the mounting flange.
Current examination and inspection methods require the actual removal of the tube from the trailer chassis to a dedicated test bench or inspection station. Removing the tube from the trailer chassis for examination and inspection typically involves the use of a crane to remove the tubes from the trailer chassis and the use of cutting torches to remove the mounting flanges from each end of the tubes. Once the tubes are removed from the trailer chassis, the tube is moved to a test station and the mounting threads on each end of the tubes are visually inspected and thread measurements are taken. Such current methods are labor intensive and generally expensive procedures.
In an effort to improve the quality and automate the inspection process, ultrasonic examination systems have been proposed. An example of an ultrasonic cylinder examination system is the system offered by FIBA Technologies, Inc. of Millbury, Mass. The FIBA Technologies ultrasonic cylinder examination system includes an array of ultrasonic transducers mounted in a customized probe. The gas cylinder is brought to a test station or test trailer where it is rotated and the ultrasonic wall thickness measurements are taken at specific intervals in a helix pattern. The FIBA system allows re-qualification of compressed gas cylinders without having to remove the valve or remove the product. However, removal of the gas cylinder from the tube trailer and removal of the mounting is still required. Moreover, The FIBA Technologies ultrasonic cylinder examination system is designed to inspect the cylindrical and shoulder sections of the gas cylinder. It is not capable of examining the end or mounting threads.
AE/UT recertification of tubes is recognized by the United States Department of Transportation. This technique does not require removal of the tubes from the trailer. What is needed is a lower cost system and method for ultrasonic examination of the mounting threads that does not involve the removal of the tube from the tube trailer.